1. Field of the Invention
The present invention relates to thermosetting coating compositions and methods of making and using the same. More specifically, the present invention relates to epoxy-functional polyurethane resins which are useful in making coatings which can be hard and/or flexible and have a remarkable appearance.
2. Brief Description of the Prior Art
Recent advances in coating technology have provided coatings which are suitable for use over various substrates which are difficult to coat. Coatings of excellent appearance, a high order of durability and having the ability to withstand severe environmental conditions have been obtained. Among the more advanced coatings are those employed on vehicles, such as automobiles, where good appearance must be maintained over long periods despite exposure to weather and various forms of attack during use.
For some time now elastomeric material which are rubbery, and resilient materials have been used for areas which are subject to mechanical shock such as automobile bumpers and moldings, exposed corners and surfaces of industrial machines, kickplates and other areas of doors and entrances, and the like. The use of such elastomeric materials aids in providing protection against permanent structural damage, but in order to attain the desired appearance a decorative and protective coating must be applied to the surface. Conventional coatings, including those employed on rubber and similar extensible objects must have the required combination of properties. These necessary properties include: Extensibility--This property is necessary in order that the advantages of the resilient substrate can be utilized without destruction of the integrity of the surface of the coating. Tensile Strength--A high degree of tensile strength is also necessary in order to avoid rupture of the film during use. Film Stability--Certain coatings which are extensible and which have a relatively high tensile strength lose these properties upon aging and particularly if the coating is exposed to sunlight, weathering, etc. Impact resistance--The coating should have adequate impact resistance at various temperatures as encountered in extreme weather variations. Adhesion--The coating should have satisfactory adhesion to the various substrates with which it is to be employed including extensible materials such as foams, rubber and the like, and metals such as mild steel. In addition the coatings should have satisfactory intercoat adhesion with succeeding coats or with various primers which can be employed. Chemical and Humidity Resistance--This includes properties such as saponification resistance upon exposure to acids and alkalis, resistance to various solvents and resistance to atmosphere of high humidity and heat.
Still other properties which are important for commercial applicability include hardness and mar resistance which make the coating particularly suitable for hard metallic substrates. Ideally, if a coating has the hardness suitable for metal substrates and is at the same time flexible, one can use the same coating for metallic and elastomeric substrates. Such a coating is described as a universal coating.
Yet other properties which are important for commercial applicability include sprayability at high solids and low volatile organic content.
It is especially difficult to obtain the above properties in combination since, in most instance, the obtention of one or several of the properties desired requires the use of materials and formulations which under ordinary circumstances tend to make the other desired properties less satisfactory. The present invention provides coating compositions that can have desirable combinations of properties disclosed herein.